Pipe-forming method and apparatus

ABSTRACT

A pipe-forming method and apparatus wherein one pipe-forming roll at each of a number of tandem-forming stations is rotated at a first speed. The mating rolls at each station are rotated at different speeds determined by the central points of contact made by each of the rolls at a station and the metal plate being formed, thereby minimizing the effects of slippage between the other surfaces of the rolls and the metal plate and preventing the breakage of the drive shafts for the rolls.

United States Patent Inventors Shigeo Kojima;

Tsutomu Nishi; Tetsunosuke Ogo;.Tetsuo Sasaki, Kawasaki-shi, Japan Appl. No. 767,208 Filed Oct. 14, 1968 Patented Mar. 23, 1971 Assignee Nippon Kokan Kabushiki Kaishi Japan Priority Oct. 14, 1967 Japan 65893/67 PIPE-FORMING METHOD AND APPARATUS 7 Claims, 2 Drawing Figs.

US. Cl 72/181 Int. Cl B2ld 5/08 Field of Search 72/179,

[56] References Cited UNITED STATES PATENTS 226,157 4/1880 Calvert et al. 72/181 812,146 2/1906 Mellinger 72/178X 1,588,817 6/1926 Smith 72/179 1,927,501 9/1933 Rafter 72/181 Primary Examiner-Milton S. Mehr Attorney- Robert D. Flynn ABSTRACT: A pipe-forming method and apparatus wherein one pipe-forming roll at each of a number of tandem-forming stations is rotated at a first speed. The mating rolls at each station are rotated at different speeds determined by the central points of contact made by each of the rolls at a station and the metal plate being formed, thereby minimizing the effects of slippage between the other surfaces of the rolls and the metal plate and preventing the breakage of the drive shafts for the rolls.

PIPE-FORMING METHOD AND APPARATUS This invention relates to a method and apparatus for forming pipes continuously from flat metal plates.

Generally, when mass-producing pipes continuously from flat metal plates, an electro-unite process or welding process is used. When pipes are formed by successively bending the flat metal plates, various problems have arisen due to the difference in peripheral speeds at the central portion and the portions at both ends of the upper and lower plate-forming rolls (see FIG. 2). If the peripheral speeds of the upper and lower rolls are set to be equal at the central portions thereof, slippage between the rolls and the plate is produced at both end portions of the rolls (i.e., between the edge portions of the plate and the rolls). This causes internal defects in the resulting pipes. Moreover, the slippage causes a twisting stress to be produced in the axles or shafts which drive the rolls, which may eventually result in the breaking of the axles or shafts. A similar undesirable effect results when the rolls are driven such that peripheral speeds thereof are set to be equal at the end portions of the rolls (i.e., at the end portions of the metal plates). In this case, slippage occurs toward the central portrons.

The cause of these detrimental effects is due to the nature of driving systems for the upper and lower rolls. To date, no positive solution for this problem has been found although much effort has been devoted to solve theproblem. In a continuous pipe-forming production line Where the forming machines are installed in tandem, it is frequently necessary that the line be stopped due to breakage of the drive shafts or to internal defects discovered in the pipes being formed.

Therefore, the main object of the present invention is to render uniform all of the output from a pipe-forming production line to prevent accidents such as breaking of axles or drive shafts and, at the same time, to produce higher quality metal pipes.

In accordance with this invention, one of the pipe-forming rolls in each of a plurality of tandem pipe-forming stations is rotated at a first angular speed. The second mating rolls in each of the stations are rotated at different respective angular speeds, said different respective speeds being determined by the diameters of the pair of rollers at each station measured at the central points of contact made by each of the mating rolls and a metal plate to be formed, thereby rendering the outputs of each of the forming stations uniform and balancing the torques on the drive shafts for each of said rolls.

The above-mentioned and other features and objects of this invention will become apparent by reference to the following description, taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a detailed illustration of a roll drive system according to the invention; and

FIG. 2 illustrates a typical pair of mating rolls driven by the drive system of FIG. 1 for forming a metal plate according to this invention.

Referring now to FIG. 1, there is shown a drive mechanism for driving a pair of mating rolls for forming a flat metal plate into a pipe. A pair of rolls used in one step in the pipe-forming process is shown in FIG. 2, wherein l designates an upper roll, 2 designates a lower mating roll and 3 designates a flat metal plate shown in cross section. As can be readily seen from F IG. 2, there is a remarkable difference in peripheral speeds at the central and end portions of the mating rolls with respect to the speed of the metal plate which moves therebetween. Thus, slippage is caused at various points. In order to minimize the effects of the different peripheral speeds of the rolls, it was found that the rotational speeds of the rolls should be set such that they are equal at the contact points corresponding to the diameters D and d,,, of the upper and lower rolls, respectively. These contact points lie at the central point contact made by each of the respective rolls with the flat metal plate 3. In this manner it was found in practice that the slippage produced at the edge surfaces of the metal plate 3 corresponding to the.contact points D d or D d respectively, could be neglected and that this slippage has substantially no effects on the pipes after being formed. Since the metal plate is successively bent by forming stations mounted in tandem, it is seen that the central point of contact made by each of the subsequent rolls and the metal plate will vary.

In accordance with the preferred embodiment of the invention described in detail herein, the lower rolls 2 of each of the plurality of forming stations are rotated at the same angular speeds. The speed of the various upper rolls 1 will be set so that at each station the peripheral speeds at the points of contact between the rolls and the metal plate corresponding to the diameters D,,, and d are equal. The diameters D and d,,, designate the diameters of the rolls which correspond to the central point of contact made by each of the rolls with the metal plate being formed.

FIG. 1 illustrates a differential drive system for providing the desired angular rotational speeds of the various rolls according to this invention. This is a mechanical apparatus, but it should be clear that various other types of drive systems be used. The gear system of FIG. 1 is housed in a housing 4. Shaft 5 is connected to a drive motor (not shown) and is further coupled to a first-stage reduction pinion 6. Pinion gear 6 is engaged with a gear 7 which in turn is coupled to a second-stage reduction pinion 8 by means of shaft 20. Pinion gear 8 is engaged with a helical-type reduction gear which is hollow. Mounted within the hollow portion of gear 9 is a standard well-known type of differential gear arrangement comprising bevel gears 11, 21, 12 and 13. The differential gear arrangement is fixed to the gear 9 by means of a pin 10. The bevel gear 12 is coupled to an output shaft 17 via a shaft 22. Bevel gear 13 is coupled to output shaft 16 via a shaft 23 and a pair of engaged gears 14 and 15. The lower roll 2 of FIG. 2 is connected to shaft 17 and the upper roll 1 of FIG. 2 is connected to shaft 16. All of the various shafts and gears are mounted by means of bearings 18 in a manner well known in the art.

In operation, the shafts 22 and 23 connected to bevel gears 12 and 13, respectively, are rotated with exactly the same speed. The shaft 22 is coupled directly to the output shaft 17 and the shaft 23 is coupled to output shaft 16 via a gear arrangement 14, 15. For convenience, the gear arrangement 14, 15 will be referred to hereinafter as distributing gears. By varying the diameters of the distributing gears 14 and 15, the speed of rotation of upper shaft 16 may be easily and accurately adjusted to provide the proper rotational speed of the upper roll 1 according to this invention. Since the central points of contact between the roll and the metal pipe being formed will vary in subsequent ones of the tandem-forming stations, the relationship between the diameters of distributing gears 14 and 15 will vary in said subsequent forming stations in order to insure that the peripheral speeds of the rolls atthe central points of contact are equal at each station.

A simple formula for determining the relationship between the diameters of the two distributing gears, is:

where a is the diameter of the lower distributing gear 14, b is the diameter of the upper gear 15, D is the diameter of the upper roll at the desired central point of contact and zi is the diameter of the lower roll at the desired central point of contact. In this manner, it is possible to impart the desired rotational speed to each of the upper rolls at each station to thereby balance the torque on each of the rolls to minimize defects in the pipe being formed and to prevent breakage of drive shafts.

When a production line utilizing pipe-forming stations according to this invention is set up, it is seen that slippage will be caused at the end portions of the metal plate 3 since the peripheral speed of the drive rolls at this point is greater than the peripheral speed of the drive rolls at the central point of contact. This slippage will be denoted as negative slippage. Moreover, slippage in the opposite sense will occur at the points of contact between the rolls and the metal plate corresponding to the point of minimum diameter of the lower roll and maximum diameter of the upper roll. This slippage is denoted as positive slippage. It should be clear from the above description that since the speeds of rotation are equal at the central points of contact between the respective rolls and the metal plate being formed, that the positive and negative slippages will tend to cancel out and produce equal balancing torques on the drive shafts for the rolls. This is the mechanism by which the occurrences of drive shaft breakage is substantially reduced. It has also been found that the positive and negative slippage occurring in the system according to this invention is not of such a magnitude to cause damage to the resulting pipes being formed. In the system according to this invention, a gear box such as shown in FIG. 1, is mounted at each of the forming stations so that the relative speeds of the pair of forming rolls at each station is easily and accurately set to favorably balance the torques of each of the rolls.

Other well-known mechanical or electrical drive means may be provided in place of the mechanism of FIG. 1. For example motors whose speeds are electrically variable by varying either the voltage, current or frequency may be used to drive the various upper and lower rolls.

It should be clear that all of the upper rolls in a pipe-forming system may be set to rotate at the same angular speed, the speeds of the lower rolls being varied to provide a system in accordance with this invention. Modifications to the drive system to vary the speeds of the lower rolls can be easily carried out by those skilled in the art within the spirit of this invention.

We claim:

1. A method of forming pipes from flat metal plates in a system which includes a plurality of tandem-forming stations, each of said stations having a pair of mating-forming rolls, comprising the steps of:

rotating one roll at each of said stations at equal predetermined first rotational speeds; and

rotating the mating roll at each of said plurality of stations at different predetermined, fixed, rotational speeds, the rotational speeds of said mating rolls at each station being set so that at each station the peripheral speeds of the pairs of rolls are equal at the central points of contact made by each roll at said station with the plate being formed.

2. A method according to claim 1 wherein said step of rotating a mating roll at a station comprises:

rotating a shaft at said equal first rotational speed;

rotating a second shaft at one of said different rotational speeds by means of a pair of gears, the diameters of which are determined by the formula b a X dm where a is the diameter of a first distributing gear, b is the diameter of a second distributing gear, D,,, is the diameter of one roll at a station measured at said central point of contact and d,,, is the diameter of the other roll at said station measured at said central point of contact.

3. Apparatus for forming pipes from flat metal plates comprising:

a plurality of tandem-forming stations, each of said forming stations including a pair of mating rolls for forming said flat metal plate into the desired configuration;

means for rotating one of the rolls at each station at equal predetermined first rotational speeds; and

means for rotating the mating rolls at each of said stations at different predetermined, fixed, rotational speeds, so that at each station the peripheral speeds of the pairs of rolls are equal at the central points of contact made by each roll at said station with the plate being formed.

4. Apparatus according to claim 3 wherein said rotating means includes:

a differential gear mechanism having first and second output shafts;

meanscoupling said one roll to said first output shaft; a distributing gear arrangement coupled to said second output shaft for changing the speed of rotation provided by said second output shaft; and

means coupling said mating roll to the output of said distributing gear arrangement.

5. Apparatus according to claim 4 comprising a differential gear mechanism and distributing gear arrangement at each of said stations.

6. Apparatus according to claim 5 wherein said distributing gear arrangement comprises first and second gears, the ratio of the diameter of said first gear with respect to the diameter of said second gear being different at each of said stations.

7. Apparatus according to claim 5 wherein the diameters of said first and second distributing gears at each station are determined by the formula b-aX dpl where a is the diameter of a first distributing gear, b is the diameter of a second distributing gear, D,, is the diameter of one roll at a station measured at said central point of contact and d is the diameter of the other roll at said station measured at said central point of contact. 

1. A method of forming pipes from flat metal plates in a system which includes a plurality of tandem-forming stations, each of said stations having a pair of mating-forming rolls, comprising the steps of: rotating one roll at each of said stations at equal predetermined first rotational speeds; and rotating the mating roll at each of said plurality of stations at different predetermined, fixed, rotational speeds, the rotational speeds of said mating rolls at each station being set so that at each station the peripheral speeds of the pairs of rolls are equal at the centrAl points of contact made by each roll at said station with the plate being formed.
 2. A method according to claim 1 wherein said step of rotating a mating roll at a station comprises: rotating a shaft at said equal first rotational speed; rotating a second shaft at one of said different rotational speeds by means of a pair of gears, the diameters of which are determined by the formula where a is the diameter of a first distributing gear, b is the diameter of a second distributing gear, Dpl is the diameter of one roll at a station measured at said central point of contact and dpl is the diameter of the other roll at said station measured at said central point of contact.
 3. Apparatus for forming pipes from flat metal plates comprising: a plurality of tandem-forming stations, each of said forming stations including a pair of mating rolls for forming said flat metal plate into the desired configuration; means for rotating one of the rolls at each station at equal predetermined first rotational speeds; and means for rotating the mating rolls at each of said stations at different predetermined, fixed, rotational speeds, so that at each station the peripheral speeds of the pairs of rolls are equal at the central points of contact made by each roll at said station with the plate being formed.
 4. Apparatus according to claim 3 wherein said rotating means includes: a differential gear mechanism having first and second output shafts; means coupling said one roll to said first output shaft; a distributing gear arrangement coupled to said second output shaft for changing the speed of rotation provided by said second output shaft; and means coupling said mating roll to the output of said distributing gear arrangement.
 5. Apparatus according to claim 4 comprising a differential gear mechanism and distributing gear arrangement at each of said stations.
 6. Apparatus according to claim 5 wherein said distributing gear arrangement comprises first and second gears, the ratio of the diameter of said first gear with respect to the diameter of said second gear being different at each of said stations.
 7. Apparatus according to claim 5 wherein the diameters of said first and second distributing gears at each station are determined by the formula where a is the diameter of a first distributing gear, b is the diameter of a second distributing gear, Dpl is the diameter of one roll at a station measured at said central point of contact and dpl is the diameter of the other roll at said station measured at said central point of contact. 